netdev - Re: [RFC 1/2] udp: add non-linear uniform port allocation scheme option /proc/sys/net/ipv4/udp_port

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Message-Id: <200912181512.18068.opurdila@ixiacom.com>
Date:	Fri, 18 Dec 2009 15:12:17 +0200
From:	Octavian Purdila <opurdila@...acom.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Lucian Adrian Grijincu <lgrijincu@...acom.com>,
	netdev@...r.kernel.org
Subject: Re: [RFC 1/2] udp: add non-linear uniform port allocation scheme option /proc/sys/net/ipv4/udp_port_randomization

On Thursday 17 December 2009 18:00:12 you wrote:
> Le 17/12/2009 16:16, Octavian Purdila a écrit :
> > Thanks for reviewing Eric. In this thread
> >
> > http://kerneltrap.org/mailarchive/linux-netdev/2009/5/8/5667204 (ports
> > being reused too fast)
> >
> > Stephen observed that port randomization effects on same port allocation
> > frequency are explained by the birthday paradox.
> 
> But this was with TCP, not UDP. Without NAT, UDP has no timewait concept.
> 
> > The RFC suggesting port randomization recognizes this issue and suggest a
> > way to overcome it, but on a first glance it looks expensive.
> >
> > Adding a sysctl to sequencial port allocation might not be the best
> > option, but we thought of kicking the discussion about this issue with
> > this patch.
> 
> Before sending patches, you might first describe the issue ?
> 

We really didn't think this through, sorry for the noise. We don't actually 
have encountered an issue with UDP, we just extrapolated from the TCP issue we 
have seen. So, will come back on this one if we really ran into issues.
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